1. Field of the Invention
This invention relates to a communication terminal for performing radio communications, such as a mobile telephone, and a communication method thereof, and in particular to a communication terminal having a transmission-reception function conforming to a plurality of radio communication systems, such as CDMA2000 1× and CDMA2000 1×EV-DO, for performing radio communications in accordance with any of the communication systems and a communication method of the communication terminal.
2. Description of the Related Art
In recent years, a radio communication terminal such as a mobile telephone for enabling the user to use a plurality of radio networks has been in practical use. In this kind of radio communication terminal, communication quality information such as the communication speed can be displayed.
As a high-speed radio communication system, CDMA2000 1×EV-DO (1× × EVolution Data Only) is about to be put to practical use.
As for the communication quality information of the communication system of CDMA2000 1× widely available at present, determination of the reception state, etc., is based on the instantaneous values of pilot signal strength to total reception signal strength (Ec/Io), carrier to interference ratio (CIR), etc., found from the pilot signal received from a base station because change in the data communication speed depending on the location is not much noticeable.
On the other hand, the communication quality information of the communication system of CDMA2000 1×EV-DO is provided by averaging the data communication speed (DRC: Data Rate Control Bit) predicted in the radio communication terminal based on the reception state (received electric field strength), C/I (Carrier to Interference), etc., and is displayed on a display section for informing the user. (For example, refer to JP-A-2002-345019 and JP-A-2003-92782.)
This enables the user of a radio communication terminal adopting the CDMA2000 1×EV-DO communication system to precisely keep track of the communication state.
To perform data communications using a radio communication terminal, the difference between performing radio communications in accordance with the CDMA2000 1× communication system and performing radio communications in accordance with the CDMA2000 1×EV-DO communication system will be discussed in association with FIGS. 6 and 7.
FIG. 6 is a schematic representation for performing radio communications in accordance with the CDMA2000 1× communication system. FIG. 7 is a schematic representation for performing radio communications in accordance with the CDMA2000 1×EV-DO communication system.
To begin with, to perform radio communications, a link as shown in FIGS. 6 and 7 needs to be established between a base station 1 and a mobile machine (radio communication terminal) 2.
To perform radio communications in accordance with the CDMA2000 1× communication system (simply, 1× communication system), a data link and radio connection need to be established.
In contrast, to perform radio communications in accordance with the CDMA2000 1×EV-DO communication system (simply, EVDO communication system), a radio (communication) session needs to be established in addition to a data link and radio connection.
Here, the data link refers to PPP (Point to Point Protocol).
The radio connection is connection for establishing radio physical connection with a network. The radio connection is established so as to actually start data communications by allocating radio resources. If communications are not performed, the radio connection is released as required.
The communication session exists only in the EVDO communication system and is established for sharing the settings, etc., required for performing communications. The communication session is held established, whereby radio setting processing at the communication start time can be skipped.
In the EVDO communication system, when power is on, the communication session is always held and therefore an attempt is made to hold the communication session by performing reconnection processing immediately after the communication session is released.
In the EVDO communication system, if inferior radio connection is released, the communication session is not released; if a superior data link is released, the communication session must be released.
In the EVDO communication system, since the communication session is not frequently released, when the communication session is established, the parameters used for communications are transmitted to the network for establishing the communication session, and the communication session is held established regardless of whether or not the information to be communicated exists so that data communications can be performed instantly. Therefore, it takes time to establish the communication session.
More particularly, at present, in the EVDO communication system, continuous connection is specified when the power is on. Since a standby mode is based on the 1× communication system, notification of starting communications according to the EVDO communication system is made based on the 1× communication system. Therefore, communications are started in the 1× communication system and then a transition is made to the EVDO communication system.
It will take time to establish the communication session required for the EVDO communication system during the transition processing.
Thus, the data required for the communication session is previously transmitted to the network for always establishing the communication session, and only when necessary, physical radio connection is established for performing data communications. Accordingly, the communication system transition can be made with good response and speedily.
As described above, in the 1× communication system, the communication session or the like is not held and thus setting processing is performed when radio connection is established (when communications are started), but a release processing only needs to be performed when the radio connection is broken.
In contrast, in the EVDO communication system, the communication session is held and thus setting processing need not be performed when radio connection is established (when communications are started), so that prompt connection can be made.
However, in the case of terminating data communications, the communication session is released together with the superior data link, and re-establishment processing (reconnection processing) of the communication session is performed immediately after the communication session is released.
At the normal time, however, re-establishment processing is performed independently of data communications, etc., and the user may be unconscious of the establishment processing of the communication session and therefore no problem arises.
JP-A-2002-345019 and JP-A-2003-92782 are referred to as related art.
By the way, in the EVDO communication system, if a data link exists, when the power is turned off, the communication session must be released together with the data link.
In contrast, in the 1× communication system, when the power is turned off, even if radio connection is established, simple connection release processing needs only to be performed.
Likewise, in the EVDO communication system, the release processing of radio connection and the communication session is also performed, but the later communication session establishment processing is performed.
The communication session establishment processing time is longer than the time allowed for turning off the power (for example, three to five seconds).
Therefore, if the power-off method of a communication terminal in the 1× communication system in the related art is applied as it is, the protocol sequence is interrupted by forced power-off processing, etc., while the communication session is being established.